The bandwidth requirements for Lync are difficult to determine for a given customer installation especially since the nature of Lync is to change how people communicate. The starting point for understanding the network bandwidth requirements are documented on Technet and Microsoft have released a bandwidth calculator.
The bandwidth usage is determined by a number of factors, the Codec used (along with overhead), the Stream activity level and for video, the resolution/quality and frame rate.
Audio Codec Bandwidth
Audio codec | Scenarios | Audio payload bitrate | Add IP header only | Also add UDP, RTP and SRTP | Also add FEC | |||
RTAudio Wideband | Peer-to-peer | 29.0 | 45.0 | 57.0 | 86.0 | |||
RTAudio Narrowband | Peer-to-peer, PSTN | 11.8 | 27.8 | 39.8 | 51.6 | |||
G.722 | Conferencing | 64.0 | 80.0 | 95.6 | 159.6 | |||
G.711 | PSTN | 64.0 | 80.0 | 92.0 | 156.0 | |||
Siren | Conferencing | 16.0 | 32.0 | 47.6 | 63.6 | |||
The bandwidth rates are in Kbps (as are all bandwidth rates in this post) and assume 100% stream activity, which is not the normal case. (Note: The online Technet document shows KBPS (i.e. Kilo Bytes per second for the base Audio payload bitrate, it should be Kbps – reference Wikipedia)
Video Resolution Bandwidth
Video codec | Resolution | Maximum video payload bitrate | Minimum video payload bitrate |
RTVideo | Main Video CIF | 250 | 50 |
RTVideo | Main Video VGA | 600 | 350 |
RTVideo | Main Video HD | 1500 | 800 |
RTVideo | Panoramic Video | 350 | 50 |
The maximum bitrate values shown (Kbps) are applicable for maximum frame rate and maximum quality. The minimum bitrate is for 1fps. HD Video is only available for peer-to-peer sessions. By default, only SD video is allowed, to allow HD video at Global or Site level use Set-CsMediaConfiguration –Identity:Global -MaxVideoRateAllowed HD720p15m
Bandwidth usage by participant
The raw bandwidth specified above is used only when the situation requires it, in other words, depending on what individual users are doing with the session determines their bandwidth requirements.
Peer-to-Peer
- Endpoints send audio streams only when the users speak.
- Both participants receive audio streams.
- If video is used, both endpoints send and receive video streams during the entire call.
Conference
- Endpoints send audio streams only when the users speak.
- All participants receive audio streams.
- If video is used, only two endpoints send a video stream at a time (the active speaker and the previous active speaker).
- If video is used, all participants receive video streams.
Stream Activity Levels
Scenario | Media | Estimated stream activity (%) |
Peer-to-peer sessions | Audio | 61 |
Peer-to-peer sessions | Main video CIF | 84 |
Peer-to-peer sessions | Main video VGA | 83 |
Peer-to-peer sessions | Main video HD | 80 |
Peer-to-peer sessions | Panoramic video | 74 |
Conferencing | Audio | 43 |
Conferencing | Main video CIF | 84 |
Conferencing | Main video VGA | 83 |
Conferencing | Main video HD | 80 |
Conferencing | Panoramic video | 74 |
PSTN | Audio | 65 |
This is based on customer data gathered by Microsoft.
Added to the media bandwidth requirements is the requirement for control traffic in the form of Real Time Control Protocol (RTCP)
RTCP Bandwidth
Media | RTCP maximum bandwidth |
Audio | 5 |
Video | 10 |
Overall Bandwidth by session type
Combining all this information together, Microsoft have come up with a table of maximum bandwidth utilisation (with and without FEC) and also typical bandwidth utilisation.
Audio/Video Capacity Planning for Peer-to-Peer Sessions
Media | Codec | Typical stream bandwidth | Maximum stream bandwidth without FEC | with FEC |
Audio | RTAudio Wideband | 39.8 | 62 | 91 |
Audio | RTAudio Narrowband | 29.3 | 44.8 | 56.6 |
Main video CIF | RTVideo | 220 | 260 | Not applicable |
Main video VGA | RTVideo | 508 | 610 | Not applicable |
Main video HD | RTVideo | 1210 | 1510 | Not applicable |
Panoramic video | RTVideo | 269 | 360 | Not applicable |
Audio/Video Capacity Planning for Conferences
Media | Typical codec | Typical stream bandwidth | Maximum stream bandwidth without FEC | with FEC |
Audio | G.722 | 46.1 | 100.6 | 164.6 |
Audio | Siren | 25.5 | 52.6 | 68.6 |
Main video CIF | RTVideo | 220 | 260 | Not applicable |
Main video VGA | RTVideo | 508 | 610 | Not applicable |
Panoramic video | RTVideo | 269 | 360 | Not applicable |
Audio Capacity Planning for PSTN
Media | Typical codec | Typical stream bandwidth | Maximum stream bandwidth without FEC | with FEC |
Audio | G.711 | 64.8 | 97 | 161 |
Audio | RTAudio Narrowband | 30.9 | 44.8 | 56.6 |
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